Glutamate is one of the major excitatory neurotransmitters that is widely spread in the brain. First indication of its role as an excitatory messenger was in the 1950's when it was observed that intravenous administration of glutamate induces convulsions. However, the detection of the whole glutamatergic neurotransmitter system with its various receptors did not take place before the 1970's and 1980's when numerous antagonists were developed or, as in the case of PCP and ketamine, were identified as antagonists. Finally, in the 1990's molecular biology provided the tools for the classification of the glutamatergic receptors.
N-methyl-D-aspartate (NMDA) receptors are a subtype of ionotropic glutamate receptors that mediate excitatory synaptic transmission in the brain. NMDA receptors are ubiquitously distributed throughout the brain and play a key role in synaptic plasticity, synaptogenesis, excitotoxicity, memory acquisition and learning. NMDA receptors are distinct from other major subtypes of ionotropic glutamate receptors (AMPA and kainate receptors) in that they are blocked by Mg2+ at resting membrane potentials, are highly Ca2+ permeable, and require co-activation by two distinct neurotransmitters: glutamate and glycine (or D-serine) (Traynelis S F et al., Pharmacol Rev. 2010; 62(3):405-96). The influx of Ca2+ through NMDA receptors triggers signaling cascades and regulates gene expression that is critical for different forms of synaptic plasticity including both long-term potentiation of synapse efficacy (LTP) (Berberich S et al., Neuropharmacology 2007; 52(1):77-86) and long-term depression (LTD) (Massey, P V et al., J Neurosci. 2004 Sep. 8; 24(36):7821-8).
The vast majority of the mammalian NMDA receptors form a heterotetramer made of two obligatory GluN1 units and two variable GluN2 receptor subunits encoded by the GRIN1 gene and one of four GRIN2 genes, respectively. One or both GluN2 subunits can be potentially replaced by a GluN3A or a GluN3B subunit. The GRIN1 gene product has 8 splice variants while there are 4 different GRIN2 genes (GRIN2A-D) encoding four distinct GluN2 subunits. The glycine binding site is present on the GluN1 subunit and the glutamate binding site is present on the GluN2 subunit.
The GluNR2 subunits play a dominant role in determining the functional and pharmacological properties of the NMDA receptor assembly and exhibit distinct distribution in different areas of the brain. For instance, GluN2B subunits are expressed primarily in the forebrain in the adult mammalian brain (Paoletti P et al., Nat Rev Neurosci. 2013; 14(6):383-400; Watanabe M et al., J Comp Neurol. 1993; 338(3):377-90) and are implicated in learning, memory processing, mood, attention, emotion and pain perception (Cull-Candy S et al., Curr Opin Neurobiol. 2001; 11(3):327-35).
Compounds that modulate GluN2B-containing NMDA receptor function can be useful in treatment of many neurological and psychiatric disorders including but not limited to bipolar disorder (Martucci L et al., Schizophrenia Res, 2006; 84(2-3):214-21), major depressive disorder (Miller O H et al., eLife. 2014; 3:e03581; Li N et al., Biol Psychiatry. 2011; 69(8):754-61), treatment-resistant depression (Preskorn S H et al. J Clin Psychopharmacol. 2008; 28(6):631-7) and their mood disorders (including schizophrenia (Grimwood S et al., Neuroreport. 1999; 10(3):461-5; Weickert C S et al. Molecular Psychiatry (2013) 18, 1185-1192), ante- and postpartum depression, seasonal affective disorder and the like), Alzheimer's disease (Hanson J E et al., Neurobiol Dis. 2015; 74:254-62; Li S et al., J Neurosci. 2011; 31(18):6627-38) and other dementias (Orgogozo J M et al. Stroke 2002, 33: 1834-1839), Parkinson's disease (Duty S, CNS Drugs. 2012; 26(12):1017-32; Steece-Collier K et al., Exp Neurol. 2000; 163(1):239-43; Leaver K R et al. Clin Exp Pharmacol Physiol. 2008; 35(11): 1388-94), Huntington's chorea (Tang T S et al., Proc Natl Acad Sci USA. 2005; 102(7):2602-7; Li L et al., J Neurophysiol. 2004; 92(5):2738-46), multiple sclerosis (Grasselli G et al., Br J Pharmacol. 2013; 168(2):502-17; Farjam M et al., Iran J Pharm Res. 2014; 13(2):695-705), cognitive impairment (Wang D et al. 2014, Expert Opin Ther Targets Expert Opin Ther Targets. 2014; 18(10):1121-30), head injury (Bullock M R et al., Ann N Y Acad Sci. 1999; 890:51-8), spinal cord injury, stroke (Yang Y et al., J Neurosurg. 2003; 98(2):397-403), epilepsy (Naspolini A P et al., Epilepsy Res. 2012 June; 100(1-2):12-9), movement disorders (e.g. dyskinesias) (Morissette M et al., Mov Disord. 2006; 21(1):9-17), various neurodegenerative diseases (e.g. amyotrophic lateral sclerosis (Fuller P I et al., Neurosci Lett. 2006; 399(1-2):157-61) or neurodegeneration associated with bacterial or chronic infections), glaucoma (Naskar R et al. Semin Ophthalmol. 1999 September; 14(3):152-8), pain (e.g. chronic, cancer, post-operative and neuropathic pain (Wu L J and Zhuo M, Neurotherapeutics. 2009; 6(4):693-702), diabetic neuropathy, migraine (Peeters M et al., J Pharmacol Exp Ther. 2007; 321(2):564-72), cerebral ischemia (Yuan H et al., Neuron. 2015; 85(6):1305-18), encephalitis (Dalmau J. et al., Lancet Neurol. 2008; 7(12):1091-8.), autism and autism spectrum disorders (Won H. et al., Nature. 2012; 486(7402):261-5), memory and learning disorders (Tang, Y. P. et al., Nature. 1999; 401(6748):63-9), obsessive compulsive disorder (Arnold P D et al., Psychiatry Res. 2009; 172(2):136-9.), attention deficit hyperactivity disorder (ADHD) (Dorval K M et al., Genes Brain Behav. 2007; 6(5):444-52), PTSD (Haller J et al. Behav Pharmacol. 2011; 22(2):113-21; Leaderbrand K et al. Neurobiol Learn Mem. 2014; 113:35-40), tinnitus (Guitton M J, and Dudai Y, Neural Plast. 2007; 80904; Hu S S et al. 2016; 273(2): 325-332), sleep disorders (like narcolepsy or excessive daytime sleepiness, patent WO 2009058261 A1), vertigo and nystagmus (Straube A. et al., Curr Opin Neurol. 2005; 18(1): 11-4; Starck M et al. J Neurol. 1997 January; 244(1):9-16), anxiety autoimmunological disorders like neuropsychiatric systemic lupus erythematosus (Kowal C et al. Proc. Natl. Acad. Sci. U.S.A. 2006; 103, 19854-19859) and addictive illnesses (e.g. alcohol addiction, drug addiction) (Nagy J, 2004, Curr Drug Targets CNS Neurol Disord. 2004; 3(3):169-79.; Shen H et al., Proc Natl Acad Sci USA. 2011; 108(48):19407-12).
In view of the clinical importance of NR2B, the identification of compounds that modulate NR2B receptor function represents an attractive avenue into the development of new therapeutic agents. Such compounds are provided herein.